Titanium dioxide is used in various fields such as optics, pigment, semiconductor, catalyst, ultraviolet blocking agent, polymer filler and ceramics since it is chemically and physically stable. In particular, if the titanium dioxide becomes nano-sized particles, its specific surface area and the number of particles are largely increased, giving it various applications such as photocatalyst, ultraviolet blocking agent, or filler for transparent polymer materials, and the like. For example, when one spherical micron size particle is divided into nano-sized particles, the number of particles can be increased to 1 billion and its specific surface area is increased a million times. Therefore, the UV blocking effect by nano-sized particles is increased (about a billion times) and its catalytic property may be increased to 1 million times that of nano-sized particles of the same weight.
However, if the specific surface area of particles is largely increased, it is accompanied by an increase of the surface tension thereof in the same condition. As a result, the particles may be easily coagulated, which results in an increase of particle size. Since the nano-sized particles are metastable, the state of such particles are unstable. On the other hand, such unstable particles can be easily adsorbed and adhered onto the surface of other bodies.
The point of zero charge of titanium dioxide particles' surface that suppresses coagulation of the particles in a solution is acidic. For this reason, a strong acidic solution dispersed with titanium dioxide particles has been prepared so as to prevent the titanium dioxide particles from coagulating. This strong acidic property restricts the use of the colloid solution containing dispersed titanium dioxide particles or the solution containing dispersed macro particles, and causes a dangerous problem to the working environment or workers.
A method of manufacturing a neutral titanium dioxide solution to solve the above problems has been developed, but this method is comprised of several steps, such as precipitating titanium dioxide in the aqueous solution, filtering the precipitates and then drying, and re-dispersing it in the solvent by an ultrasonic method or vigorous mechanical stirring method. However, because it is impossible to re-ground and re-disperse the coagulated nano-sized particles by using an ultrasonic method or stirring method, and the filtering step is a time consuming procedure, its productivity is very low and the cost of production is very high. Furthermore, the nano-sized particles can be easily re-coagulated at a little higher temperature, thus a transparent colloid solution which is uniformly dispersed with nano-sized particles of less than 10 nm could not be produced by this method.
Furthermore, due to such a coagulation phenomenon, less than 3% of titanium dioxide can be dispersed in the conventional titanium dioxide colloid solution. Such low concentration of titanium dioxide colloid solution causes serious problems of cost, applicability or productivity, etc., due to difficulties in transportation, storage or production.
The present invention provides a method of manufacturing a colloid solution which is dispersed with nano-sized titanium dioxide particles in one step without performing conventional multi-steps, including the filtering or re-dispersing steps. More particularly, the present invention provides a colloid solution which is 1˜5% by weight of dispersed titanium dioxide which is superior to the conventional colloid solution, which is 1˜3% by weight of dispersed titanium dioxide.
The titanium dioxide colloid solution prepared by the present method is a high concentration (3˜5% by weight) and neutral solution, thus its application field can be greatly extended.